This invention relates to identification cards and in particular to machine engraved identification cards.
Engraved identification cards are known and can be made utilizing any one of a number of available electronic engraving systems such as that disclosed in Noda, et al., U.S. Pat. No. 3,950,608 or Wada et al., U.S. Pat. No. 4,052,739 or any other engraving system. Utilizing an electronic engraving system, an image can be engraved in an identification card blank by making a multiplicity of scores through one opaque colored plastic layer of the card blank into a second different colored opaque plastic layer of the card blank. By altering the depth of the scoring, the width of the region between scores can be continuously varied to generate light and dark regions which make up the desired image. A complete description of such prior art identification cards and the method of making them is disclosed in Oka, et al., U.S. Pat. No. 3,897,964 and Oka et al., U.S. Pat. No. 3,930,924.
As indicated, however, such identification cards required an opaque base of one color overlaid with an opaque layer of a contrasting color so that light impinging on the engraved surface of the card is variably reflected back to the eye of the observer according to the location and amount of the top layer removed to expose the bottom layer to form an observable image.
By contrast, the present invention provides a translucent base with but a single colored layer which is disposed across one surface of the translucent base. Engraving occurs through the colored layer into the translucent base to variably expose the translucent base. Background light then passes through the translucent base material in only those regions not covered by the opaque regions, i.e., where the opaque layer has not been removed by the engraving process.
The image is therefore a result of the contrast between the background light passing through the translucent base in those regions where the single colored layer has been removed and the light reflected from the front of the card in the regions where the colored layer has not been removed. This is in contrast to prior art cards which rely solely upon the variable reflectivity of light from the two opaque layers on the front of the engraved card. Thus, in prior art cards, background light is irrelevant.
A surprising and particular advantageous feature of the present invention is that both a "negative" and a "positive" image can be observed on the novel identification card in accordance with the invention even though only a single image is engraved. By way of explanation, because the image observed depends on the contrast between the background light passing through the translucent base and the foreground light reflecting off of the colored layer on the front of the card, when the amount of background light is below a certain level, the engraved image looks like a photographic negative whereas when the background light is above a particular level then the engraved image looks like a photographic positive.
This dual image effect provides an inherent security feature whereby the authenticity of a particular card can be tested without special equipment or user training. For example, if the engraved image is removed from the card by scraping the engraved surface of the identification card and then printing another image on the card, the above-described dual image effect will not be created. Hence, such a counterfeit card will be readily discernible simply by holding the identification card up to the light. By contrast, prior art identification cards can be altered by scraping the engraved region of the card, printing or substituting a new image on the card, and then making scores across the printed or substituted image to simulate an engraved surface.